DM9161BIEP DAVICOM [Davicom Semiconductor, Inc.], DM9161BIEP Datasheet - Page 16

• Manufacturer Part Number: DM9161BIEP
• Description: Industrial-grade 10/100 Mbps Fast Ethernet Physical Layer Single Chip Transceiver
• Manufacturer: DAVICOM [Davicom Semiconductor, Inc.]

The block diagram in figure 7-3 provides an overview of the
functional blocks contained in the transmit section.
The transmitter section contains the following functional
blocks:
- 4B5B Encoder
- Scrambler
- Parallel to Serial Converter
- NRZ to NRZI Encoder
- NRZI to MLT-3
- MLT-3 Driver
7.2.1.1 4B5B Encoder
The 4B5B encoder converts 4-bit (4B) nibble data generated
by the MAC Reconciliation Layer into a 5-bit (5B) code group
for transmission, see reference Table 7-1. This conversion is
required for control and packet data to be combined in code
groups. The 4B5B encoder substitutes the first 8 bits of the
MAC preamble with a J/K code group pair (11000 10001)
upon transmit. The 4B5B encoder continues to replace
subsequent 4B preamble and
corresponding 5B code-groups. At the end of the transmit
packet, upon the deassertion of the Transmit Enable signal
from the MAC Reconciliation layer, the 4B5B encoder injects
the T/R code group pair (01101 00111) indicating end of
frame. After the T/R code group pair, the 4B5B encoder
continuously injects IDLEs into the transmit data stream until
Transmit Enable is asserted and the next transmit packet is
detected.
within the 100Base-TX Transmitter for support of
applications like 100 Mbps repeaters, which do not require
4B5B conversion.
7.2.1.2 Scrambler
The scrambler is required to control the radiated emissions
(EMI) by spreading the transmit energy across the frequency
spectrum at the media connector and on the twisted pair
cable in 100Base-TX operation.
Preliminary
Version: DM9161BI-12-DS-P01
July 16, 2008
The DM9161BI includes a Bypass 4B5B conversion option
data nibbles with
Industrial-grade 10/100 Mbps Fast Ethernet Physical Layer Single Chip Transceiver
By scrambling the data, the total energy presented to the
cable is randomly distributed over a wide frequency range.
Without the scrambler, energy levels on the cable could
peak beyond FCC limitations at frequencies related to
repeated 5B sequences like continuous transmission of
IDLE symbols. The scrambler output is combined with the
NRZ 5B data from the code group encoder via an XOR logic
function. The result is a scrambled data stream with sufficient
randomization to decrease radiated emissions at critical
frequencies.
7.2.1.3 Parallel to Serial Converter
The Parallel to Serial Converter receives parallel 5B
scrambled data from the scrambler and serializes it
(converts it from a parallel to a serial data stream). The
serialized data stream is then presented to the NRZ to
NRZI encoder block
7.2.1.4 NRZ to NRZI Encoder
Since the transmit data stream has been scrambled and
serialized, the data must be NRZI encoded for compatibility
with the TP-PMD standard for 100Base-TX transmission
over Category-5 unshielded twisted pair cable.
7.2.1.5 MLT-3 Converter
The MLT-3 conversion is accomplished by converting the
data stream output from the NRZI encoder into two binary
data streams with alternately phased logic one events.
7.2.1.6 MLT-3 Driver
The two binary data streams, created at the MLT-3 converter,
are fed to the twisted pair output driver, which converts these
streams to current sources and alternately drives either side
of the transmit transformer’s primary winding, resulting in a
minimal current MLT-3 signal. Refer to figure 7-4 for the
block diagram of the MLT-3 converter.
DM9161BI
16